This invention relates generally to ink jet apparatus, and more specifically to a transducer array for use in a multi-jet, drop-on-demand ink jet printer.
In liquid droplet ejecting systems of the drop-on-demand type, such as impulse ink jet printers, a piezoceramic transducer is used to cause expulsion of ink as droplets from a small nozzle or jet. An array of such jets is often utilized in high-speed, high-resolution printers where, as is well-known, the printing rate and printed image resolution is dependent upon the number of jets and spacing therebetween. In general, the closer the jets are to one another, the faster the images can be produced and the higher the resulting image resolution.
One suitable such printer is described in U.S. Pat. No. 4,459,601, issued July 10, 1984 to Stuart D. Howkins, assigned to the assignee of the present invention and incorporated herein by reference. In that arrangement, an ink jet apparatus of the demand or impulse type comprises a chamber and an orifice from which droplets of ink are ejected in response to the state of energization of a transducer which communicates with the chamber through a foot forming a movable wall. The transducer expands and contracts, in a direction having at least one component extending parallel with the direction of droplet ejection through the orifice, and is elongated in such direction, the electric field resulting from the energizing voltage being applied transverse to the axis of elongation.
One problem common to all high-speed, high resolution, drop-on-demand ink jet printers occurs because the jets of an array are spaced very close to one another. That is, the response of a one jet in an array to its drive voltage can be affected by the simultaneous application of a drive voltage to another nearby jet. This can result in a phenomenon, known in the art as "mechanical cross-talk", where pressure waves are transmitted through the solid material in which the jets are formed, or in another phenomenon, known in the art as "electrical cross-talk", where relatively large drive voltages necessary for substantial displacement of transducers utilized in the prior art cause the subsequent pulsing of an inappropriate jet.
While the risk of electrical cross-talk between ink jets in an array utilizing the teachings of U.S. Pat. No. 4,459,601 as discussed above will be minimized, the risk of mechanical cross-talk remains. One approach which alleviates this problem, however, is discussed in U.S. Pat. No. 4,439,780, issued Mar. 27, 1984 to Thomas W. DeYoung and Viacheslav B. Maltsev, assigned to the assignee of the present invention and incorporated herein by reference. In that arrangement, an ink jet array comprises a plurality of elongated transducers coupled to a plurality of ink jet chambers, the transducers being supported only at their longitudinal extremities. The support at the extremity remote from the chamber is provided such that no longitudinal motion along the axis of elongation of the transducers occurs, while the support at the other extremity includes bearings which substantially preclude lateral movement of the transducers transverse to their axis of elongation but permit the longitudinal movement thereof along the axis, thus minimizing mechanical cross-talk between jets within the array.
Other characteristic problems which are encountered in the implementation of high-speed, high-resolution impulse ink jet printers do not impact so much upon their operation, but indeed impact upon their fabrication. For example, the relatively small sizes of transducer elements used in densely packed arrays make them difficult to handle. A unitary transducer array is, therefor, preferred.
One early approach towards the resolution of the above-described problem is disclosed in U.S. Pat. No. 4,072,959, which issued to Rune Elmqvist. As discussed therein, a recorder operating with drops of liquid includes a comb-shaped piezoelectric transducer arranged such that individual teeth of the comb are associated respectively to a densely-packed array of ink jet chambers. In this connection, it will be appreciated that the chambers are quite small so as to produce a high Helmholtz frequency as compared with the longitudinal resonant frequency of the individual transducers. Such a relationship can be undesirable since it is difficult to damp the longitudinal resonant frequency.
As is also discussed in the Elmqvist patent, each of the transducers is immersed in a common reservoir such that energization of one transducer associated with one chamber may produce cross-talk with respect to an adjacent chamber or chambers. In other words, there is no fluidic isolation from chamber to chamber between the various transducers, or more accurately, segments of the common transducer. In addition to such cross-talk problems, the construction shown in the Elmqvist patent poses a requirement for a non-conductive ink.
Similar such attempts to ease the manufacture of impulse-type arrays which reduce mechanical cross-talk between individual jets are disclosed in U.S. Pat. No. 4,389,658, issued to Theodore P. Perna et al, and U.S. Pat. No. 4,446,469, issued solely to Perna. In accordance with the '658 patent, a pulsed liquid droplet ejecting apparatus array comprises a plurality of rectangular piezoelectric transducers which are arranged abaxially over ink-containing chambers, an edge of each transducer being fixed against a reaction block. An improved method for rigidly mounting the piezoelectric transducers to the reaction block, comprising a cross-talk reducing member installed between adjacent transducers, is taught by U.S. Pat. No. 4,446,469. The U.S. Pat. No. 4,446,469 cross-talk reducing member is made up of two steel plates held in spaced relationship by adhesive, forming a void therebetween to reduce transmittal of pressure waves from one transducer to another. Both of these patents, nevertheless, require tedious picking and placing operations during their fabrication.
One other approach to the simplification of assembly operations in the manufacture of ink jet printers is disclosed in U.S. Pat. No. 4,409,601, issued to Kenth Nilsson et al, and U.S. Pat. No. 4,539,575, issued solely to Nilsson. In accordance with the '601 patent, a mosaic recorder for ejecting liquid droplets has nozzles arranged in rows in front of a recording medium, each nozzle having a piezoelectric transducer associated therewith. The individual transducers are comprised of bilaminar teeth of a comb-like piezoplate consisting of a piezoceramic and a carrier material, the piezoplate having a base by which the transducers are attached to a recording head. For reducing the mechanical coupling between the transducer teeth so that transmission of coupling forces from an activated transducer tooth to the adjacent transducer teeth is substantially eliminated, the ceramic material between the teeth in the area of the comb base is removed so as to provide a gap between adjacent teeth. While the unattached ends of each transducer in the '601 patent are arranged to provide flexural vibration to excite the respective nozzle, the '575 patent teaches the use of individual, bilaminar transducer elements which are connected at both ends via cross pieces. Upon application of an electrical potential, the excited transducer lifts away from the jet plate in a quasi-arcuate fashion, subsequently returning to a flat configuration thereby ejecting a drop through the jet orifice. While perhaps satisfactory for many applications, neither of the patents described immediately above solve the many problems associated with manufacturing transducer elements for incorporation into impulse ink jet printers.